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Method for Receiving Data Sent in a Sequence in a Mobile Radio System with
Reception Gaps

Abstract

Methods for receiving data sent by a first emitter of a mobile telephony
system to a first resource element of a resource, via a receiver,
radiopockets being created during the reception, and data which is not
received during the creation of the radiopockets being reconstructed by
the receiver are provided. The data which is not received by the first
emitter is received by a second emitter, in a temporarally offset manner,
on the same resource element of the resource, between the radiopockets,
and is used to reconstruct the sequence of data. A conversion is
especially advantageous for carrying out a receiving method in UMTS
compression mode during the reception of data which is sent continuously
independently of the compression mode.

19. A method for receiving a set of data elements by a receiver in a
mobile radio system, comprising: receiving a first transmission from a
first transmitter on a first resource element of a resource, the first
transmission comprising a first set of data elements and a reception gap,
the first data set in a first order; receiving a second transmission from
a second transmitter on the first resource element, the second
transmission comprising a second set of data elements and a reception
gap, the second data set in a second order; and constructing from the
first and second data sets a third data set by replacing a missing
element due to the gap in the first transmission, wherein the first and
second data sets are subsets of the third data set.

20. The method as claimed in claim 19, wherein the elements in the second
data set are in a different order than corresponding elements within the
third data set.

21. The method as claimed in claim 19, wherein the second data set is
received with a time offset from the receipt of the first data set such
that a missing element due to the gap in the second transmission is a
different missing element due to the gap in the first transmission.

22. The method as claimed in claim 19, wherein the resource element is a
transmit and receive frequency.

23. The method as claimed in claim 22, wherein the reception gaps are
produced as a result of a temporary changeover of the resource element by
the receiver to another resource element of the resource.

24. A method for sending a data set from a second transmitter to a
receiver in a mobile radio system, a first transmitter sending a set of
data elements in a first sequence to the receiver via a resource element
of a resource, a first element of the data set not received on the
receiver side due to a reception gap during the reception of the data
set, the method comprising: sending the data set by the second
transmitter on the same resource element so that a second element not
received on the receiver side due to a reception gap during a reception
of the data set from the second transmitter is not the same as the first
element.

25. The method as claimed in claim 24, wherein the order of the elements
in the data set sent by the second transmitter is different than the
order of the elements in the data set sent by the first transmitter.

26. The method as claimed in claim 25, wherein the order of the data
elements is transposed during the transmission by the second transmitter
with respect to the order of the data elements during the transmission
via the first transmitter in each case a limited number of elements is
transmitted.

27. The method as claimed in claim 26, wherein the limited number of
elements is four and in each case a set of no more than four sequence
orders is used in the mobile radio system.

29. The method as claimed in claim 24, wherein the data set sent by the
second transmitter is sent with a time offset with respect to the
transmission via the first transmitter.

30. The method as claimed in claim 29, wherein the offset of a data
element during the transmission via the second transmitter with respect
to the transmission of the data element via the first transmitter
corresponds to: at least twice a duration of the reception gap or a sum
of a duration of the reception gap and the current or maximum time shift
between the transmitters.

31. The method as claimed in claim 24, wherein the mobile radio system is
a communication system with the resource element for sending the data
sets over a period of time and the receiver temporarily interrupts the
reception during the period of time for the purpose of receiving on
another resource element and thereby causes the reception gaps.

32. A receiver system for a mobile radio system, comprising: a receiver
device for receiving a sequence of data elements on a first resource
element of a resource; a reception gap produced in the received sequence
of data elements when the receiver device temporarily interrupts the
reception on the resource element for the purpose of temporarily changing
to a second resource element; and a data element not received during the
reception gap being received after a time offset from a second
transmitter and processed to reconstruct the sequence of data.

33. The receiver system as claimed in claim 32, wherein performing a
reception method in the UMTS compression mode method upon reception of
data sent continuously and without taking the compression mode into
account.

34. The receiver system s claimed in claim 32, wherein the offset does not
exceed the duration of one frame to enable a timely reconstruction.

35. Devices of a mobile radio system, comprising: a sequence of data
elements; and a plurality of transmitters with at least partially
overlapping transmitting areas, the transmitters transmitting the data
elements, the transmitters embodied to use the same resource element of a
resource in each case for transmitting the data elements, one transmitter
of the plurality of transmitters being embodied to transmit data elements
in each case with an offset with respect to a corresponding data element
on a different transmitter.

36. The devices as claimed in claim 35, wherein the plurality of
transmitters are sector transmitters of a single transmitting station.

37. The devices as claimed in claim 35, wherein the offset does not exceed
the duration of one frame to enable a timely reconstruction of the
sequence of data elements by a receiver.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is the US National Stage of International
Application No. PCT/EP2005/051944, filed Apr. 28, 2005 and claims the
benefit thereof. The International Application claims the benefits of
German application No. 102004022146.4 DE filed May 5, 2004 and German
application No. 102004029444.5 DE filed Jun. 18, 2004, all of the
applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

[0002] The invention relates to a method for receiving data sent in a
sequence in a mobile radio system with reception gaps, to a method for
sending a sequence of data from a transmitter to at least one receiver in
a mobile radio system of said type, and to a communication system having
at least two transmitters.

BACKGROUND OF INVENTION

[0003] In a mobile radio system, conforming, for example, to the Universal
Mobile Telecommunication System (UMTS) standard, communication
connections are set up via radio interfaces between mobile subscriber
stations (UE: User Equipment) and stationary base stations (Node B). In
order to support the mobility of a subscriber station, the subscriber
station must continually carry out measurements with regard to a possible
transition (handover) to another base station. These measurements are
performed both in an idle state and in a connected state (connected
mode). For this reason a mode referred to as compressed mode (CM) was
introduced in UMTS in the FDD (Frequency Division Duplex) operating mode
in order to enable a subscriber station to perform inter-frequency and
inter-RAT (Radio Access Technology) measurements also during an existing
connection to a dedicated channel (DCH) even without a second receiving
device. With only one receiving device the subscriber station can perform
e.g. handover measurements to a GSM radio access network (GSM: Global
System for Mobile Telecommunication) during an existing connection.
According to the present specification different types of compressed
operating modes can be configured by the network. The first operating
mode is referred to as "Uplink (UL) in CM only". This operating mode for
an uplink connection in compressed mode only is advantageous, for
example, if a terminal or, as the case may be, a subscriber station is
equipped with a second receiving device, but said subscriber station has
to perform measurements in, for example, the GSM 1800 frequency band
close to the UMTS frequency band on which an existing connection is being
maintained to the first receiving device. In such a case a continuous
transmission of the subscriber station on a dedicated UMTS channel (UE
UMTS DCH Transmission) would cause strong interference with the GSM
measurements which are performed using the second receiving device.

[0004] A second operating mode is used in the compressed operating mode
for uplink and downlink connections and is referred to as UL/DL CM (DL:
Downlink). This operating mode is used in order to be able to avoid the
requirement for a second receiving device in the subscriber station and
also for a second synthesizer. The third operating mode for downlink
connections in compressed mode only, which is referred to as "DL in CM
only", can be used if a single receiving station with two synthesizers is
used in order to perform, for example, inter-RAT measurements in the GSM
900 frequency band (GSM 900 Inter RAT Measurements).

[0005] FIG. 2 illustrates the principle of the compressed operating mode.
Data is transmitted via a plurality of frames fr, whereby currently
between one and a maximum of seven slots per frame fr can be occupied by
the subscriber station for the purpose of performing the measurements.
These timeslots can be situated either in the middle of the individual
frame fr or be distributed over two frames fr. The transmit power P is
increased in the compressed frame frc, thereby maintaining the quality of
the connection constant. A compressed frame of this kind therefore
consists of compressed data cd and a gap G. During the gap G the
subscriber station can perform a measurement on other resources, in
particular other frequencies. Which of the frames fr, frc are compressed
is decided by the network or, as the case may be, communication system.
Compressed frames frc can be specified periodically or also on request.
The rate and type of the compressed frames frc are variable and depend,
for example, on the type of measurements to be performed by the
subscriber station. The structure of the compressed operating mode is
assigned to a specific subscriber station, the structures generally being
different between different subscriber stations of a plurality of
subscriber stations within a cell. In the compressed operating mode data
is therefore transmitted by way of frames fr, some of said frames frc
having, as compressed frames frc, transmission gaps G in which no data is
sent.

[0006] Also provided for a communication system of this kind are
multimedia broadcast transmissions and what are called multicast services
(MBMS: Multimedia Broadcast and Multicast Service), this being a service
in which the base stations transmit information of general interest on a
commonly used channel. This shared channel is monitored by a plurality of
subscriber stations. The general information can be similar, for example,
to teletext in television or to the content which is transmitted via DAB
(Digital Audio Broadcasting), but also includes services such as
multimedia. Such a service can be used, for example, to transmit news of
goals in a football match to a plurality of subscriber stations over a
single channel. During the transmission over this channel, however, a
continuous transmission of data without transmission gaps is planned.
During the time of the reception gaps on the receiving station side, no
corresponding transmission gaps are provided on the side of the
transmitting station with MBMS, with the result that a data loss occurs
during the reception gaps.

[0007] With the introduction of MBMS for UMTS the problem therefore arises
that the physical channel (S-CCPCH) that is used for MBMS does not
support the compressed operating mode (CM). In the cases in which a
subscriber station is in a dedicated connection state it is clear that at
the instants in which the subscriber station performs measurements in the
case of a compressed operating mode, data which is transmitted at this
time in the corresponding S-CCPCH frames is lost. This results in a loss
of MBMS data which is transmitted in continuous sequence over the channel
S-CCPCH. In this case the amount of lost data is dependent on the length
of the gaps, the frequency of the gaps and the number of active CM
sequences in the subscriber station.

[0008] FIG. 3 shows an example of data structures such as are received by
a subscriber station over a dedicated connection in the compressed
operating mode via what is referred to as a DPCH channel (DPCH: Dedicated
Connection in CM) in the top illustration. The bottom diagram shows which
data is received or, as the case may be, not received by the subscriber
station as receiver in the operating mode with reception gaps in the case
of the reception of continuous data over such a broadcast channel S-CCPCH
during the reception of MBMS. The subscriber station performs various
measurements, for example a measurement of the received signal strength
of GSM signals (GSM RSSI: Signal Strength Indicator). Further
measurements are performed, for example, with regard to a base station
identification code BSIC and with regard to inter-FDD frequencies. It is
clear that during these measurement times data on the channel S-CCPCH is
lost if the subscriber station has only a single receiver device and must
therefore change the reception frequency.

[0009] A similar problem arises if a subscriber station is in a forward
directed access channel state of a cell (Cell FACH (Forward Access
Channel) state) in which the subscriber station is assigned a generally
specified or a subdivided transport channel in the uplink direction, the
random access channel (RACH) for example, which the subscriber station
can use for the access procedure at any time. Access to the FACH of the
cell is characterized in that the position of the subscriber station is
known to the UMTS terrestrial radio access network (UTRAN: UMTS
Terrestrial Radio Access Network) at cell level with regard to the cell
in which the subscriber station last executed a cell update procedure. In
this state no permanently dedicated channel is assigned to the subscriber
station and measurements in accordance with the compressed operating mode
are not required. Nonetheless the subscriber station must continuously
monitor the FACH in the downlink direction and inter-frequency and
inter-RAT measurements need to be performed periodically. The duration of
the measurement cycle corresponds to the duration of the largest
transmission time interval (TTI) on the channel S-CCPCH used for the
broadcast messages or, as the case may be, MBMS which can be observed by
the subscriber station, the measurement sequences taking place
periodically every 2.sup.k transmission time intervals, where k=1,2,3 for
80 ms TTI conforming to current specifications. In the case of a TTI
measurement duration of 80 ms as the longest duration there are
measurement periods of 160 ms, 320 ms or 640 ms, according to the choice
of k. For illustration purposes FIG. 4 shows an example of a subscriber
station in what is referred to as the cell FACH state with k=2. Every 320
ms the subscriber station can interrupt the MBMS reception on the
corresponding channel S-CCPCH in case inter-frequency and RAT
measurements are required.

[0010] A disadvantage with all the methods is that in the case of the
compressed operating mode a subscriber station can only incompletely
receive continuously and successively sent data on a channel S-CCPCH.
Various approaches to solving the problem are currently under discussion.
One approach consists in a transmitter with knowledge of the gaps on the
receiving subscriber station side simply interrupting the transmission of
MBMS data during these times and performing a discontinuous transmission
(DTX).

[0011] Another approach consists in the subscriber station on the receiver
side attempting to reconstruct missing data, for example by performing a
decoding using a forward error correction (FEC) technique, e.g. using
turbo-decoding and interleaving methods known per se. However, these
approaches are problematic, since the measurement gaps of different
receiver-side subscriber stations which are located within a cell and
receive and MBMS data are not aligned with one another in respect of
time. The corresponding structures of the gaps are measurement-specific,
i.e. dependent on the type of measurement which is to be performed by a
subscriber station, in other words, for example, inter-frequency or
inter-RAT measurements, while this also depends, for example, on the
position of the subscriber station within the cell.

[0012] The preferred approach at the present time is for the subscriber
station to perform inter-frequency or inter-RAT measurements during an
MBMS reception using discontinuous reception (DRX). In this case the MBMS
data is sent and transmitted without interruption, with an individual
receiving subscriber station simply losing the MBMS data which was not
received during the time that inter-frequency and inter-RAT measurements
were being performed. Said subscriber station would have to attempt to
reconstruct the missing data through the use of a forward error
correction method.

SUMMARY OF INVENTION

[0013] An object of the invention is to propose an alternative and
preferably improved method for receiving a sequence of sent data during
reception gaps in the reception or, alternatively, to propose a
correspondingly suitable method for sending a sequence of data, a
receiver and a corresponding communication system.

[0014] This object is achieved by a method for receiving data sent in a
sequence, by a method for sending a sequence of data, by a receiver for a
mobile radio system and by mobile radio system devices according to the
independent claims.

[0015] Accordingly, a method is preferred for receiving, by means of a
receiver, data sent in a sequence by a first transmitter of a mobile
radio system on a first resource element of a resource, wherein reception
gaps occur during the reception and data not received during the
reception gaps is reconstructed by the receiver, wherein the data not
received from the first transmitter is received offset in time or in
scrambled form from a second transmitter on the same resource element of
the resource between the reception gaps and used for reconstructing the
sequence of data.

[0016] Accordingly, alternatively or in combination, a method is preferred
for sending a sequence of data from a transmitter to at least one
receiver in a mobile radio system via a resource element of a resource,
wherein the mobile radio system has a second transmitter with a
transmitting area overlapping the transmitting area of the first
transmitter, wherein the data is sent with an offset on the same resource
element by the second transmitter offset in time or in scrambled form
with respect to its transmission via the first transmitter in such a way
that data not received on the receiver side due to reception gaps on the
resource element during the reception of the data from the first
transmitter can be reconstructed.

[0017] Accordingly, a receiver for a mobile radio system is preferred
having a receiver device for receiving a sequence of data of a
transmitter on a resource element of a resource, wherein the receiver
device temporarily interrupts the reception on the resource element for
the purpose of temporarily changing the resource element, as a result of
which reception gaps are produced, with data not received during a
reception gap being received from a second transmitter with a time offset
and processed in order to reconstruct the sequence of data.

[0018] Accordingly, mobile radio system devices of a mobile radio system
are preferred having at least two transmitters with at least partially
overlapping transmitting areas, wherein the transmitters transmit a
sequence of data, wherein the transmitters are embodied for using the
same resource element of a resource in each case to transmit the data,
wherein one transmitter of the transmitters is embodied to transmit
individual data elements or data blocks of the data in each case with an
offset with respect to a corresponding data element or data block on or,
as the case may be, compared to the other transmitter.

[0019] Advantageous embodiments are the subject matter of dependent
claims.

[0020] A method is particularly preferred wherein a transmit and receive
frequency is used as the resource element, in particular a frequency of
an FDD or FDMA mobile radio system.

[0021] A method is particularly preferred wherein the reception gaps on
the receiver side are produced by a temporary changeover of the resource
element to another resource element of the resource.

[0022] An approach of this kind is also transferable to other data
outages, for example if individual data elements or blocks of a sequence
of data cannot be received due to interference, such as, for example, in
the case of a second receiver device and active measurements in a near
frequency band with too high an interference effect. The method can also
be implemented in the case of external interferences caused by an
external interference source.

[0023] A method is particularly preferred wherein the mobile radio system
is a communication system having the resource element for sending the
sequence of data over a period of time and the at least one receiver
interrupts the reception during the period of time temporarily in order
to receive on a different resource element and thereby causes the
reception gaps.

[0024] A method is particularly preferred wherein the order of the data,
in particular data blocks during the transmission by the second
transmitter, is transposed compared with the order of the data during the
transmission via the first transmitter in each case within data blocks
with a limited number of elements. A transposition of this kind, i.e. a
permutation, can be performed cyclically or randomly in sub-areas.

[0025] If the transmitters are synchronized, e.g. within the sectors of a
cell, a simple cyclical transposition of data sub-areas, ideally as small
as possible, thus prevents the same data being transmitted by a plurality
of transmitters at any time and in addition the memory required for
resorting the data in the receiving device is small. Furthermore, if data
packets with packet numbers for identifying the order are present, a
simple reordering can be performed. If merely temporal shifts are
performed while the order of the individual data elements remains the
same, then it is also possible for the purposes of comparison, by finding
a corresponding data element, to perform a cross-correlation between the
data sequence with missing data element and the data sequence from the
other transmitter.

[0026] The shift or, as the case may be, scrambling used by adjacent
stations is preferably communicated to the mobile station. This can be
done either by means of explicit signaling or is implicitly transmitted
by means of another characteristic quantity, e.g. the cell identification
ID. For example, the shift used can be calculated from the cell ID modulo
a maximum shift value, or the number of the permutation applied for the
scrambling can be calculated from the cell ID modulo the number of
permutations used.

[0027] If, however, the transmitters are not synchronized, it is
preferable that no purely cyclical transpositions are performed since in
this way it is not possible, in the event of an arbitrary random time
shift between two transmitters, to prevent the situation occurring in
which the same data is transmitted at the same time by both transmitters.
In this case a permutation, in particular a random permutation, of data
sub-areas that are as small as possible can be performed, with the result
that once again the memory required for the resorting in the receiving
device is small.

[0028] Such a method is particularly preferred wherein an offset of a data
element or data block of the data during the transmission via the second
transmitter relative to the transmission of said data element or data
block via the first transmitter corresponds to at least twice the
duration of the reception gap.

[0029] Such a method, such a receiver or such mobile radio system devices
are particularly preferred for performing a reception method in the UMTS
compression mode method when receiving data sent continuously and without
taking the compression mode into account.

[0030] Such a method, such a receiver device or such a mobile radio system
device are particularly preferred wherein the first and the second
transmitter are two sector transmitters of a single transmitting station.

[0031] Such a method, such a receiver device or such a mobile radio system
device are particularly preferred wherein the offset enables a timely
reconstruction, in particular does not exceed the duration of one frame.

[0032] Either the offset is zero with regard to e.g. sectors of a cell or
completely random. The cyclical transposition relates not to the entire
data stream, but only to parts, in particular parts that are as small as
possible.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] An exemplary embodiment is explained in more detail below with
reference to the drawing, in which:

[0038] A selective combining (SC) reception by a subscriber station UE is
preferred. For this purpose the same data content, i.e. the same data or
data packets, is sent in adjacent sectors and/or cells by more than one
base station to a subscriber station. In this case no restrictions are
imposed in respect of the synchronization of the data itself. The
subscriber station performs inter-frequency or inter-RAT measurements in
a known manner in, for example, the compressed operating mode according
to UMTS and cannot receive all the data on one MBMS channel. However, the
data which was sent and not received during the measurement gaps or, as
the case may be, reception gaps is reconstructed. In addition to the
possibility of a forward error correction (FEC) mechanism known per se,
this is realized in that the data or data packets are sent in adjacent
and overlapping sectors and/or cells with an offset or at times that are
interleaved with respect to one another. This enables the subscriber
station to receive data not received during a reception gap via the same
resource at an offset time from an adjacent cell or from an adjacent
sector and to use said data for the reconstruction.

[0039] FIG. 1 shows in schematic form an arrangement of different devices
of a mobile radio system, conforming to UMTS for example, as well as data
transmitted therein between stations. In principle, however, it is
possible to transfer said arrangement to other mobile radio systems and,
where applicable, other operating modes with comparable problems. In
particular, in addition to the use of two separate base stations B1, B2
each having its own cell c1 and c2 respectively, it is also possible to
use a single base station having a sector antenna array and sector cells.

[0040] Specifically, three base stations B1, B2, B3 are shown as
transmitters by way of example. They are connected to a central control
device CC and are controlled centrally with regard to the transmission of
data and the setting up of communication connections. In UMTS said
central control devices can be the so-called RNCs (Radio Network
Controllers).

[0041] One subscriber station serves as the receiver UE and is located in
the overlapping area of the cells c1 and c2 of the first and second
transmitter B1, B2 respectively. A dedicated connection exists between
the receiver UE and the first transmitter B1. The receiver UE is in an
operating mode in which mainly data on a first frequency as a first
resource element f1 of the resource frequency of the FDD method is
received from the first transmitter B1. In between times the receiver UE
switches for short moments of time to a second resource element f2, i.e.
to a second frequency, in order to perform measurements there. During
this period of time no data b of a sequence of data a, b, c, d, e can be
received which is transmitted over the first frequency f1 by the first
transmitter B1. The sequence of data a-e consists of data elements or
data blocks which are to be transmitted by the first transmitter B1 over
a broadcast channel at the first frequency as resource element f1 to a
plurality of subscriber-side receivers UE. The receiver UE is therefore,
for example, a subscriber station in the UMTS compressed operating mode,
which subscriber station receives MBMS data from the first transmitter
B1.

[0042] The receiver UE is also located within the radio range of the
second transmitter B2. The second transmitter B2 sends the same data of
the sequence of data a-e to receiver UE in the area of its cell c2. In
order to be able to compensate for the reception gaps at the receiver UE
as a result of its operation in the compressed operating mode, the second
transmitter B2 sends, on the preferably same resource element f1, i.e.
the same first frequency, said data of the sequence of data a-e with a
time offset, e.g. scrambled, with respect to the corresponding
transmission by the first transmitter B1. As a result there is a high
probability that the receiver UE can receive the missing data b from the
second transmitter B2 owing to the time scrambling.

[0043] The scrambling can be effected in a number of different ways. In
addition to a temporally shifted transmission of the individual data
elements or data blocks of the sequence of data a-e at a different time
by the two transmitters B1, B2, the order during the transmission of the
individual data elements or data blocks of the sequence of data a-e can
also be transposed. Such a transposition can be performed cyclically or
randomly.

[0044] In the choice of the offset for the purpose of offset transmission
of the data by the second transmitter B2, the duration of the reception
gap is preferably taken into account. The offset will be chosen to be
proportionally greater than the duration of a reception gap. An offset of
at least twice the reception gap is particularly preferred.

[0045] In a further embodiment the offset is chosen to be at least as
great as to be equivalent to the sum of the reception gap and the current
or maximum time shift between two adjacent transmitters. It is then
ensured that a reception gap cannot adversely affect the reception of a
data packet from both transmitters.

[0046] Such an approach is also advantageous with regard to the problems
of the transmit power consumption on the part of the transmitters B1, B2
during the sending of data of a sequence of data a-e over MBMS channels
in order to reduce the required power. This too is advantageously made
possible by the selective choice of data of different transmitters on the
part of the receiver UE. The transmission of the sequence of data a-e for
the different adjacent and mutually overlapping sectors or cells c1, c2
is coordinated with regard to the content in MBMS by the network, for
example the central control device CC. However, the synchronization
requirements for the selective combining to be performed in such a way
are not very strict compared to the maximum ratio combining in the area
of at least some TTIs.

[0047] In the case of a coordinated or, as the case may be, synchronous
transmission, e.g. within the sectors of a cell, the reconstructability
on the part of the receiver UE is advantageously increased by a
transposition of the data to be sent in the manner of a pairwise
permutation. In the case of such a pairwise permutation, the sequence {a,
b, c, d, e, f}, for example, is transmitted by the first transmitter,
while the second transmitter B2 transmits the pairwise permutated
sequence {b, a, d, c, f, e}. This offers the advantage that only a very
small amount of data buffering is required for the reordering on the part
of a receiver which regularly receives the data of the second transmitter
B2 and must therefore reorder all the received data. Already with
simultaneous transmission of a frame containing a plurality of such data
elements or, as the case may be, by the other transmitter of a frame
containing said data, this data, however, permutated in pairs, this
pairwise permutation offers a high degree of security against the loss of
a data element or data block on the same S-CCPCH MBMS TTI during an
inter-frequency or inter-RAT measurement.

[0048] If the transmitters B1, B2 are not coordinated in time with regard
to the transmission times, a random permutation of the data elements is
advantageous. This ensures that in any event a data reconstruction of the
transmitters B1, B2 and a length of 1 MBMS S-CCPCH TTI is made possible
if the selective combining during the transmission of the data offset in
such a way via two transmitters B1, B2 is received. For example, a
permutation can be used wherein the permutated sequence is transmitted by
the second transmitter B2. The permutation is performed using the
sequence of the first transmitter B1, with four or more data elements or
data blocks being permutated among one another in each case. Data element
1 is shifted to position 3, data element 2 to position 4, data element 3
to position 1, and data element 4 to position 2. In order to break up
cyclical behavior, elements are additionally permutated between the
described groups with four or more data elements.

[0049] The scrambling or permutation of the data elements or the delay for
the individual transmitters can be performed by the individual
transmitters (or components assigned thereto). However, it can also be
performed centrally by a central control device CC (for example RNC) for
all the transmitters controlled by this control device. The latter
alternative has the advantage that this function must be implemented in
comparatively few network elements, in particular the memory required for
the scrambling or permutation or delay must also only be made available
in these elements.

[0050] In a further exemplary embodiment it is also possible to specify a
set of sequence orders (permutations). At any instant in time each base
station is allocated a sequence order from this set, the sequence orders
being changed at regular intervals. Advantageously the sequence orders
are chosen randomly or pseudo-randomly, i.e. using a pseudorandom number
algorithm which makes the choice deterministically as a function of
certain parameters, the cell ID and the current frame number, for
example. Because adjacent cells randomly select sequence orders it is
ensured that irrespective of the time offset of the transmissions a
minimum probability is ensured that the transmissions of a data packet
from the two cells can be used for the reconstruction. In this case the
probability is dependent on the number of sequence orders (at least
provided the sequence orders are suitably chosen, as also described
further below). With, for example, 4 sequence orders the minimum
probability is 75% (since sequence orders which lead to a simultaneous
transmission of the data packet in question are chosen only in a quarter
of the cases). This method thus leads to a statistical averaging of the
collisions and in particular prevents such events occurring continually
at specific locations.

[0051] This exemplary embodiment has the advantage that the cells do not
need to be synchronized in time and also that no coordinated planning has
to be carried out for the allocation of sequence orders.

[0052] Typically, individual cells in a network are synchronized, e.g.
sectors which are radiated from a common location, whereas others are
unsynchronized, e.g. sectors at other locations. The method can also be
advantageously employed in this case: a common (pseudo-)random number
generator is used for the synchronized cells; a cell-specific offset
value is then added to the value supplied by said generator, the value
range of the random number generator being equal to the number of
sequence orders and the addition being performed with the offset value
modulo the number of sequence orders. The offset values must be allocated
here in such a way that adjacent cells receive different offset values.
However, as the number of synchronized cells is typically small in the
cited scenario, in particular much smaller than the total number of cells
in the network, this allocation is easily and locally plannable. Planning
with regard to the unsynchronized cells, more particularly network-wide
planning is not necessary. In this way it is ensured that adjacent
synchronized cells always use different sequence orders and at the same
time a statistical averaging effect as described above occurs with
adjacent unsynchronized cells.

[0053] In a realistic system there are typically more cells c1, c2 than of
two transmitters B1, B2 or, as the case may be, sectors. In order to
ensure that the adjacent cells in such a case have different scrambling
schemes or permutations, at least four sequence orders are used.
According to the known four-color theorem any geographical map can be
colored using four colors in such a way that adjacent regions have
different colors, which means that sequence orders can also be allocated
to the cells such that adjacent cells always use different sequence
orders. In this way it is ensured that any subscriber station UE which
receives two such adjacent cells can reconstruct missing data.

[0054] Such a set of 4 sequence orders containing 4 elements is, for
example, the following set (sequence order set 1):

{a,b,c,d},

{d,a,b,c},

{c,d,a,b},

{b,c,d,a}

[0055] It can be seen that the elements a to d each occur once per row and
column. This is necessary because each data packet must be sent precisely
once by each cell (row) and because at any instant in time the data
packet is sent by precisely one cell so that it is guaranteed that a UE
which receives two cells but cannot receive at one instant can receive
the data packet again. If the minimum spacing between the transmissions
of the data packets via the different cells should have to be greater so
that a reception can be guaranteed, then the criterion that each element
only occurs precisely once per column is not adequate. It is therefore
clear that a set of sequence orders with a length of 4 can contain no
more than 4 sequence orders (more generally, a set of sequence orders
with a length n, where the spacing between the transmissions of the data
packets via the different cells must be greater than m, can contain a
maximum of n/m sequence orders).

[0056] This special set of sequence orders has the property that the
sequence orders are cyclically transposed with respect to one another. As
already described, sets of sequence orders of arbitrary length can be
generated easily by cyclical transposition. The maximum number of
possible sequence orders per set depends on the length of the sequence
orders and the minimum spacing between the transmissions of a data packet
on the different cells. By suitable selection of these parameters it is
therefore always possible to find a suitable set.

[0057] A further set of 4 sequence orders with 4 elements is the following
set (sequence order set 2):

{a,b,c,d},

{b,a,d,c},

{c,d,a,b},

{d,c,b,a}

[0058] This set is characterized in that the second sequence is the
pairwise permutation of the first sequence, and the fourth sequence is
the pairwise permutation of the third sequence. As already shown,
pairwise permutated sequences have the advantage that only a very small
amount of data buffering is required. However, it is not possible to form
a set of more than two sequences, with all sequences being pairwise
permutated sequences among themselves. To that extent the sequence order
set 2 is optimal insofar as it contains at least two pairs of pairwise
permutated sequences.

[0060] Continue the sequences analogously, as a result of which two
pairwise permutated sequences of length 4 are produced (other letters are
used for the continuation, i.e. c is used instead of a, and d instead of
b, in order to obtain unique designations):

{a,b,c,d},

{b,a,d,c}

[0061] Append further sequences n, the appended sequences being formed
from the existing sequences by transposition of the first and second half
(in this case the sequence {c,d,a,b} is produced from {a,b,c,d} because
the halves "a,b" and "c,d" are transposed), thereby yielding the sequence
order set 2):

{a,b,c,d},

{b,a,d,c},

{c,d,a,b},

{d,c,b,a}

[0062] Using this law of formation, sets of sequence orders can be
generated whose length is a power of two, e.g. next is the set of length
8:

{a,b,c,d,e,f,g,h},

{b,a,d,c,f,e,h,g},

{c,d,a,b,g,h,e,f},

{d,c,b,a,h,g,f,e},

{e,f,g,h,a,b,c,d},

{f,e,h,g,b,a,d,c},

{g,h,e,f,c,d,a,b},

{h,g,f,e,d,c,b,a}

[0063] A further set of 4 sequence orders containing 4 elements, which set
likewise contains two pairs of pairwise permutated sequences (and which
is therefore also optimal in the above-mentioned sense) is the following
set (although this set is somewhat less "elegant" as it is not so
symmetrical) (sequence order set 3):

{a,b,c,d},

{b,a,d,c},

{d,c,a,b},

{c,d,b,a}

[0064] Disregarding renamings of the elements and row transpositions,
there are therefore in total only four sets of 4 sequence orders
containing 4 elements, the still missing set being (sequence order set
4):

{a,b,c,d}, {c,a,d,b}, {b,d,a,c}, {d,c,b,a}

[0065] All these four sets can preferably be used in mobile radio systems,
the sequence order set 2 being characterized in particular as a pair of
pairwise transposed sequences and by the symmetrical law of formation,
though the sequence order set 3 is equivalent (apart from the law of
formation, which is, however, only of secondary importance as regards
performance).